Fix Linux build issues. gtest compilation failure, test flag, and copying local configs to install directory

[ethanmoffat]

• google test failed to compile since the CXX standard was set after the google test project was included
• test flag on linux was only printing the name of the test exe instead of running tests
• added copy for local configs (config_local directory) on install target

[iandinwoodie]

@ethanmoffat I also updated the linux build script to have the -t --test option in the help message and to inform users that they must perform a build and install to run tests (see commit d8136fb).

So, with the new default behavior you can successfully run:

./build-linux.sh --clean --test

However, if you try to run tests on a clean build without an install:

./build-linux.sh --clean --no-install --test

Then you'll get the following error and notice:

Error: the test runner "/home/ird/dev/EndlessOpenSource/etheos/install/test/eoserv_test" does not exist.
Notice: you must build and install to run tests.

GitHub's review process won't let you approve these changes via their review process (since you are the PR opener). However, for the sake of consistency with our "approve before merge" policy, maybe you could signal your approval via a comment in the PR for commits 9211b87 and d8136fb.