fix(zfspv): mounting the volume if it is ready

[pawanpraka1]

Signed-off-by: Pawan pawan@mayadata.io

Why is this PR required? What issue does it fix?:

Instead of checking for the finalizer, checking for the
volume state to be ready is more intuitive before mounting it.

Also removed duplicate if statement for btrfs which was added while resolveing
the merge conflict in #175.

Checklist:

• Fixes #
• PR Title follows the convention of <type>(<scope>): <subject>
• Has the change log section been updated?
• Commit has unit tests
• Commit has integration tests
• (Optional) Are upgrade changes included in this PR? If not, mention the issue/PR to track:
• (Optional) If documentation changes are required, which issue on https://github.com/openebs/openebs-docs is used to track them:

[codecov-commenter]

Codecov Report

Merging #184 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #184   +/-   ##
=======================================
  Coverage   22.88%   22.88%           
=======================================
  Files          14       14           
  Lines         485      485           
=======================================
  Hits          111      111           
  Misses        373      373           
  Partials        1        1           

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