disk/api.py: resize2fs fails silently + adds tests

+ The method disk.api.resize2fs fails silently and should
  writes some information in the log.
+ Adds missing tests to disk.api.resize2fs

Change-Id: I4edd88fb85a73c75628958e3f2ea668c0d3cad89
Closes-Bug: #1270088
Merge "disk/api.py: resize2fs fails silently + adds tests"