Remove reference to 'in-use' state in share manager

State 'in-use' is leftover from Cinder and is not used by shares,
hence it should be removed.
Due to absense of tests for this module at all, as part of bug fix
were added unittests.

Change-Id: I768d731bac3eb1f420695082e69598e55e1de90b
Closes-Bug: #1346371
Partial-Bug: #1348635
Merge "Remove reference to 'in-use' state in share manager"