Setup environment for Intel Parallel Studio

Set up the environment for the Intel compilers and tools. This commit
does the following:

- Unset variables that were incorrect from the auto guess prefix
  inspections.
- Add a RemovePath environment_modifications_formats for dotkit.
- Set the module environment variables appropriate for the different
  variants.
- Change the component logic so that the '+all' variant works. It was
  getting split by letter and leaving COMPONENTS empty.
- Added a variant checking function.
- Added NONRPM_DB_DIR to the silent.cfg so that the product database
  goes to the installation directory.
- With the product database in prefix the code to remove the product
  database file from the home directory is no longer needed and was
  removed.
- Reformat the 'tools' variant description.

There are probably more variables needed for the '+tools' for the
'professional' product version but I do not have access to that.

lib/spack/spack/modules.py

@@ -471,6 +471,7 @@ class Dotkit(EnvModule):
     path = join_path(spack.share_path, 'dotkit')
     environment_modifications_formats = {
         PrependPath: 'dk_alter {name} {value}\n',
+        RemovePath: 'dk_unalter {name} {value}\n',
         SetEnv: 'dk_setenv {name} {value}\n'
     }