quantum-plugin-nicira imports mock but was not used

The import of mock prevents quantum from starting when using the
nvp plugin since mock is not an install dependency. This patch
removes where mock was imported but did not actually need to be.

Fixes bug 1097451

Change-Id: If1569d437fe523e4fac8d686da52b0508ca1cbf3
Correct exception output for subnet deletion when port is used

Fixes bug 1093754

Change-Id: I2deaced0cfc2524234ff79e39e6e7c2f757ff19f
Merge "quantum-plugin-nicira imports mock but was not used" into stable/folsom
Merge "Correct exception output for subnet deletion when port is used" into stable/folsom