Add macro for ros1/2 finding gtest and gmock

[ross-desmond]

The macro find_common_test_packages will use ament or catkin to link to gtest and gmock libraries.

Note: You must add dependencies on gtest and gmock in the package.xml still

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 #30 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #30   +/-   ##
=======================================
  Coverage   89.51%   89.51%           
=======================================
  Files          16       16           
  Lines         820      820           
=======================================
  Hits          734      734           
  Misses         86       86

Flag	Coverage Δ
#ROS_1	89.51% <ø> (ø)	⬆️
#ROS_2	?
#bouncy	?
#crystal	?
#kinetic	89.61% <ø> (ø)	⬆️
#lunar	89.61% <ø> (ø)	⬆️
#melodic	91.84% <ø> (ø)	⬆️

---

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Δ = absolute <relative> (impact), ø = not affected, ? = missing data
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[codecov]

Codecov Report

Merging #30 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #30   +/-   ##
=======================================
  Coverage   89.51%   89.51%           
=======================================
  Files          16       16           
  Lines         820      820           
=======================================
  Hits          734      734           
  Misses         86       86

Flag	Coverage Δ
#ROS_1	89.51% <ø> (ø)	⬆️
#ROS_2	?
#bouncy	?
#crystal	?
#kinetic	89.61% <ø> (ø)	⬆️
#lunar	?
#melodic	91.84% <ø> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update d8d7189...4aee1ca. Read the comment docs.

[timrobotson]

When using the latest commit I'm getting errors about being unable to find gmock:

CMake Warning at /opt/ros/kinetic/share/catkin/cmake/test/gtest.cmake:149 (message):
  skipping gmock 'test_aws_log_system' in project 'aws_common' because gmock
  was not found
Call Stack (most recent call first):
  /opt/ros/kinetic/share/catkin/cmake/test/gtest.cmake:79 (_catkin_add_executable_with_google_test)
  /opt/ros/kinetic/share/catkin/cmake/test/gtest.cmake:54 (_catkin_add_google_test)
  cmake/DefineTestMacros.cmake:48 (catkin_add_gmock)
  CMakeLists.txt:67 (add_common_gtest)

Using commit f25d518ef4113e0e7e6ac50a3eb076f03d89c94b works for me.