improves lvm version parsing for customised builds

supports_thin_provisioning now uses a regexp to ensure parsing of
lvm version succeeds when the build is customised; also adds a test
for a customised string parsing

Closes-Bug: #1237994
Change-Id: I49049a58bbdb5315b9d2d7c259a9324ca15d78cb
Merge "improves lvm version parsing for customised builds"