Make libstatssocket shared

Also make private versions of the libraries available to link statically
for tests. We should try to figure out a better long term solution.

Test: m
Test: bit statsd_test:*
Test: atest LibStatsPullTests
Test: bit libstatssocket_test:*
Test: atest GtsStatsdHostTestCases
Bug: 149340100

Change-Id: I05b91efab2a657aec75d436575aff4373f86ed3f