New option: SCALAPACK_BUILD_TESTS

[derpda]

Allow users to choose whether they want to build tests or not.

See #29 for some initial discussion.
By default, tests are build as was the case before this PR.
By using cmake -DSCALAPACK_BUILD_TESTS=OFF, users can turn off building tests and save on build time.
The same was possible by specifying a target (make scalapack), but giving a cmake option is good practice I believe.

Note that PBLAS/TIMING is also considered a "test" and is thus not build when SCALAPACK_BUILD_TESTS is turned off by the user.

Miscellaneous

I also deleted some spaces at the end of several lines (automatically, many editors like vim do this).

[langou]

Thanks @derpda