Removed eval of unchecked strings.

Removed eval of unchecked strings.

 * eval() was previously used to marshall unchecked strings as
   filter parameters for QuantumDbPluginV2.get_ports() via
   the --fixed_ips flag.
 * This change removes the use of eval and cleans up the filtering
   implementation for get_ports().
 * The new filtering implementation does not support arbitrary
   OR'ing or AND'ing.  Instead, multiple values for a given filter
   key are logically OR'ed, and filters across keys are AND'ed.
 * Example usage - filter for .2 or .3 in the given subnet:

     quantum port-list -- --fixed_ips ip_address=10.0.0.3 \
         ip_address=10.0.0.2 subnet_id=nOtaRealId

 * Addresses bug 1052179

Change-Id: I451f33ae53e623f86015b3fc2e6a7ca2f51ee836