profiler: add test against go master branch.
profiler: add test against go master branch.

Allow AgentIntegration test to run in parallel to prevent timeout when
testing against master.

Change-Id: I2d3c992ee09d349a6deaaade72a81724550e76a3
Reviewed-on: https://code-review.googlesource.com/c/37510
Reviewed-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Alexey Alexandrov <707c85aa1ca9cc766e4957d3fb95a91b4e895454@google.com>
Reviewed-by: Jianqiao Li <2d515f767da37bdb8a87cabf23e3e650ab8dc69c@google.com>

googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go