yum deadlocks during the build

Brief Description
-----------------
Occasionally mock hangs during the build due to a stale yum.lock file in the chroot directory. This is caused by a bug in pre-DNF yum-builddep: it creates the pid file, but never deletes it. If the stale PID happens to match an existing process during a subsequent yum run, it thinks the file is locked and hangs.

Severity
--------
Minor

Steps to Reproduce
------------------

Call build-pkgs on a CentOS 7 host or docker container.

Expected Behavior
------------------
Mock, yum & related commands called by build-pkgs work correctly.

Actual Behavior
---------------
Yum deadlocks.

Reproducibility
---------------
Intermittent. Happens very infrequently.

System Configuration
--------------------
CentOS 7 - based build host

Branch/Pull Time/Commit
-----------------------
Master branch, 2021-03-22

Last pass
---------
N/A

Timestamp/Logs
--------------

DEBUG package_manager.py:96: ['/usr/bin/yum-builddep', '--installroot', '/localdisk/loadbuild/jenkins/WRCP_Dev_Build/2021-03-20_00-00-07/rt/mock/b0/root/', '--releasever', '7', '/localdisk/loadbuild/jenkins/WRCP_Dev_Build/2021-03-20_00-00-07/rt/mock/b0/root//builddir/build/SRPMS/wrs_avp-kmod-rt-1.2.14-0.tis.2.src.rpm']
DEBUG util.py:563: child environment: None
DEBUG util.py:495: Executing command: ['/usr/bin/yum-builddep', '--installroot', '/localdisk/loadbuild/jenkins/WRCP_Dev_Build/2021-03-20_00-00-07/rt/mock/b0/root/', '--releasever', '7', '/localdisk/loadbuild/jenkins/WRCP_Dev_Build/2021-03-20_00-00-07/rt/mock/b0/root//builddir/build/SRPMS/wrs_avp-kmod-rt-1.2.14-0.tis.2.src.rpm'] with env {'LANG': 'en_US.UTF-8', 'BUILD_DATE': '2021-03-20 02:19:06 -0400', 'TERM': 'vt100', 'SHELL': '/bin/bash', 'LC_MESSAGES': 'C', 'WRS_GIT_BRANCH': 'HEAD', 'HOSTNAME': 'mock', 'REPO': '/localdisk/designer/jenkins/WRCP_Dev_Build/cgcs-root', 'CGCS_GIT_BRANCH': 'HEAD', 'PROMPT_COMMAND': 'printf "\x1b]0;<mock-chroot>\x07<mock-chroot>"', 'PATH': '/usr/bin:/bin:/usr/sbin:/sbin', 'HOME': '/builddir', 'BUILD_BY': 'jenkins'} and shell False
DEBUG util.py:417: http://127.0.0.1:8088/localdisk/loadbuild/jenkins/WRCP_Dev_Build/2021-03-20_00-00-07/installer/rpmbuild/RPMS/repodata/repomd.xml: [Errno 14] HTTP Error 404 - Not Found
DEBUG util.py:417: Trying other mirror.
DEBUG util.py:417: To address this issue please refer to the below wiki article
DEBUG util.py:417: https://wiki.centos.org/yum-errors
DEBUG util.py:417: If above article doesn't help to resolve this issue please use https://bugs.centos.org/.
DEBUG util.py:417: Getting requirements for wrs_avp-kmod-rt-1.2.14-0.tis.2.src
DEBUG util.py:417: --> Already installed : gcc-4.8.5-36.el7.x86_64
DEBUG util.py:417: --> Already installed : glibc-headers-2.17-317.el7.x86_64
DEBUG util.py:417: --> Already installed : kernel-rt-devel-3.10.0-1127.rt56.1093.el7.tis.8.x86_64
DEBUG util.py:417: --> Already installed : 4:perl-5.16.3-299.el7_9.x86_64
DEBUG util.py:417: --> Already installed : 1:openssl-1.0.2k-16.el7.x86_64
DEBUG util.py:417: --> Already installed : elfutils-libelf-devel-0.176-2.el7.x86_64
DEBUG util.py:417: Error: No Package found for cgcs-dpdk-rt
DEBUG util.py:417: Error: No Package found for cgcs-dpdk-rt-dev
DEBUG util.py:542: Child return code was: 1
DEBUG util.py:176: kill orphans
...
DEBUG util.py:495: Executing command: ['/usr/bin/yum', '--installroot', '/localdisk/loadbuild/jenkins/WRCP_Dev_Build/2021-03-20_00-00-07/rt/mock/b3/root/', '-y', '--releasever', '7', 'update'] with env {'LANG': 'en_US.UTF-8', 'BUILD_DATE': '2021-03-20 02:19:06 -0400', 'TERM': 'vt100', 'SHELL': '/bin/bash', 'LC_MESSAGES': 'C', 'WRS_GIT_BRANCH': 'HEAD', 'HOSTNAME': 'mock', 'REPO': '/localdisk/designer/jenkins/WRCP_Dev_Build/cgcs-root', 'CGCS_GIT_BRANCH': 'HEAD', 'PROMPT_COMMAND': 'printf "\x1b]0;<mock-chroot>\x07<mock-chroot>"', 'PATH': '/usr/bin:/bin:/usr/sbin:/sbin', 'HOME': '/builddir', 'BUILD_BY': 'jenkins'} and shell False
DEBUG util.py:417: Existing lock /localdisk/loadbuild/jenkins/WRCP_Dev_Build/2021-03-20_00-00-07/rt/mock/b3/root/var/run/yum.pid: another copy is running as pid 68378.
DEBUG util.py:417: Another app is currently holding the yum lock; waiting for it to exit...
DEBUG util.py:417: The other application is: mock
DEBUG util.py:417: Memory : 16 M RSS (268 MB VSZ)
DEBUG util.py:417: Started: Sat Mar 20 02:35:19 2021 - 00:01 ago
DEBUG util.py:417: State : Running, pid: 68378
DEBUG util.py:417: Another app is currently holding the yum lock; waiting for it to exit...
DEBUG util.py:417: The other application is: mock
DEBUG util.py:417: Memory : 16 M RSS (268 MB VSZ)
DEBUG util.py:417: Started: Sat Mar 20 02:35:19 2021 - 00:03 ago
DEBUG util.py:417: State : Sleeping, pid: 68378
...