Enable disabled CtsFsMgrTestCases test cases

And use the new fs_mgr C++ API.

Bug: 186504948
Test: atest CtsFsMgrTestCases
Test: atest CtsFsMgrTestCases in DSU
Change-Id: I80d68d72fb3aa9f5a0dc7d9400b4d0f80cc7deb3
1 file changed