Modify cloudwatch common to depend on gtest, gmock

[ross-desmond]

Use the macro in aws_common to find test dependencies for ROS1 or ROS2.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

Merging #19 into master will increase coverage by 3.17%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #19      +/-   ##
==========================================
+ Coverage   84.18%   87.35%   +3.17%     
==========================================
  Files          21       22       +1     
  Lines        1018      981      -37     
==========================================
  Hits          857      857              
+ Misses        161      124      -37

Flag	Coverage Δ
#ROS_1	87.35% <ø> (+3.17%)	⬆️
#kinetic	?
#melodic	87.35% <ø> (-0.54%)	⬇️

Impacted Files	Coverage Δ
...atch_metrics_common/src/metric_manager_factory.cpp	0% <0%> (ø)
cloudwatch_logs_common/test/log_manager_test.cpp	100% <0%> (+5.47%)	⬆️
cloudwatch_logs_common/test/log_publisher_test.cpp	85.88% <0%> (+9.84%)	⬆️
...dwatch_logs_common/test/cloudwatch_facade_test.cpp	100% <0%> (+12.14%)	⬆️
cloudwatch_logs_common/test/shared_object_test.cpp	100% <0%> (+26.82%)	⬆️

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