Fix FindNETCDF.cmake with libnetcdff not present.

FindNETCDF.cmake seemed to have trouble on some systems (specifically
pleiades) due to CMake syntax issues. This is fixed by removing some
quotation marks from the build, preventing extra whitespace from being
added to certain flags.

Additionally, this commit switches back to using find_library to set the
library flags. Hopefully this will prevent any other whitespace issues,
since CMake itself is constructing these variables. However, the
find_path calls are also kept, and used to provide hints to the
find_library calls, in the hope that this will cause netCDF
installations containing static libraries to be preferred when they are
available.

This change was tested by running short CESM cases, which were
successful on pleiades, yellowstone, titan, and mira.