BUG: Include find GTest CMake code when installed

[blowekamp]

May address: #303

PR Checklist

• [ ] No API changes were made (or the changes have been approved)
• [ ] No major design changes were made (or the changes have been approved)
• [ ] Added test (or behavior not changed)
• [ ] Updated API documentation (or API not changed)
• [ ] Added license to new files (if any)
• [ ] Added Python wrapping to new files (if any) as described in ITK Software Guide Section 9.5
• [ ] Added ITK examples for all new major features (if any)

Refer to the ITK Software Guide for further development details if necessary.

[blowekamp]

The GTest libraries should not be a build time dependency of an installed ITK, but not sure how to disable the GTest libraries in an installed ITK.

[bradking]

not sure how to disable the GTest libraries in an installed ITK.

One needs to make sure nothing depends on them publicly. Then they shouldn't need to be installed.

[blowekamp]

not sure how to disable the GTest libraries in an installed ITK.

One needs to make sure nothing depends on them publicly. Then they shouldn't need to be installed.

In all "itk-module.cmake" files, if used, it is under "TEST_DEPENDS".

[bradking]

Off the top of my head I don't see why TEST_DEPENDS in the build tree should affect requirements in the install tree, at least conceptually.

[thewtex]

@blowekamp should this be integrated?