[fuel-plugin-builder] execution of pre_build_hook depends on current directory

Detailed bug description:
fpb executes pre_build_hook from current directory. In case pre_build_hook depends on files in root directory of plugin fpb fails with error "Shell command executed with "127" exit code: lcm-plugin/pre_build_hook".
Steps to reproduce:
1. create simle plugin from examples
2. create script prebuildhook.sh in root directory of plugin with any code
3. create pre_build_hook file with next lines:
#!/bin/bash
./prebuildhook.sh
4. cd to your home dir
5. fpb --build plugin_dir
Expected results:
 fpb build plugin successfully.
Actual result:
fpb fails with next error:
"Shell command executed with "127" exit code: lcm-plugin/pre_build_hook"
Reproducibility:
always
Workaround:
do not use relative paths in pre_build_hook script. Do 'popd && cd basename $0' at start of pre_build_hook and pushd at the end.
Impact:
Description of the environment:
 Operation system: Centos 7 with fpb installed from master branch of fuel-plugins repo.
 Versions of components: latest fpb installed from master branch of fuel-plugins repo.
 Reference architecture: N/A
 Network model: N/A
 Related projects installed: N/A
Additional information:

I suggest a simple fix :

--- a/fuel_plugin_builder/actions/build.py
+++ b/fuel_plugin_builder/actions/build.py
@@ -79,7 +79,7 @@ class BaseBuildPlugin(BaseAction):

     def run_pre_build_hook(self):
         if utils.which(self.pre_build_hook_path):
- utils.exec_cmd(self.pre_build_hook_path)
+ utils.exec_cmd(self.pre_build_hook_path, self.plugin_path)

     def add_checksums_file(self):
         utils.create_checksums_file(self.build_src_dir, self.checksums_path)