Add regression_tests to the ALL target.

[andrew-platt]

Fixes issue #1325

Feature or improvement description
When BUILD_TESTING is enabled, a user would generally expect that a make install command would include everything for the regression testing. This PR adds the regression_tests target to the ALL target in the CMake build system.

Related issue, if one exists
#1325

Impacted areas of the software
This only affects the cmake build system when testing is enabled.

[deslaughter]

Adding ALL to regression_test_module_drivers isn't necessary as it's a dependency of regression_tests, but it shouldn't hurt either. I think this is ready to be merged.