Extend hashtree eqc test timeouts

The sha_test_ and eqc_test_ test suites in the hashtree module have
had trouble with slowness and timeouts on slower test machines.  Use
spawn so each test runs in its own process and extend the timeouts to
120 seconds to avoid these spurious failures.
Merge pull request #589 from basho/bugfix/hashtree-test-timeouts

Extend hashtree eqc test timeouts

Reviewed-by: reiddraper