Removes directory creation prior to _tmp_mount

Reasons:
- Directory creation is included in VolumeMountPoint.mount method.
- No need to repeat the steps before calling the mount method.

Changes:
- Removed directory creation prior to calling _tmp_mount.
- Test updated to reduce number of utils.execute,
  as we now have one less call in the code.

Change-Id: I5136f1ce537c919ff2e009cd617f33925d955e88
Closes-Bug: #1261905
Merge "Removes directory creation prior to _tmp_mount"