Create valid, unique LV names

We filter out all bad characters and bad substrings, and then check
for 'volume name already exists' errors. We make 5 attempts to generate
a unix volume suffix before finally giving up.

Fixes #12

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Make sensible temporary filenames and avoid leaking them

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Escape the name of the VG as well as the LV

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Merge pull request #13 from djs55/python-dir

Create valid, unique LV names