Fix lvol: Find LVM commands in PATH env - Bugfix Pull Request

#### Bugfix Pull Request

##### ansible version: 
ansible 1.9 (devel 704f7d7b40) last updated 2014/11/26 09:53:17 (GMT +200)
  lib/ansible/modules/core: (detached HEAD 41559311d8) last updated 2014/11/26 09:53:27 (GMT +200)
  lib/ansible/modules/extras: (lvol-env-path 317654dba5) last updated 2014/11/26 10:33:02 (GMT +200)
##### OS: CentOS 6, SLES 11

When I ran the lvol module as a non root-user with sudo, I get 

*msg: [Errno 2] No such file or directory*

for every LVM command. This PR solve the issue with module method get_bin_path.

Please review and give feedback. :thumbsup: