Support -c and -m for GTEST.

This takes the --test-class and --test-method options and builds a
--gtest_filter value to use when invoking native tests.

How it works:
ARGS to runtest                     ARG to GTEST
--test-class=    --test-method=     <none>
--test-class=Foo --test-method=     --gtest_filter=Foo.*
--test-class=    --test-method=Bar  --gtest_filter=*.Bar
--test-class=Foo --test-method=Bar  --gtest_filter=Foo.Bar

Advanced:
-m *Iptables* runs all test methods containing 'Iptables' in any class.
-c *ControllerTest runs all tests in any class ending with 'ControllerTest'.

Note that the '.' and '*' characters above are not shell globs. The '*'
are wildcards, and the '.' are literals.

Test: runtest -x system/netd/server/netd_unit_test.cpp -m '*Iptables*'
Test: runtest -x system/netd/server/netd_unit_test.cpp -c BandwidthControllerTest
Test: runtest -x system/netd/server/netd_unit_test.cpp -c BandwidthControllerTest -m '*Iptables*'
Change-Id: I967296da1bdcbc404f5ab91d24f9714eec7b475b