Start a test to exercise lustre code.

At present, the SKIPIF functionality does not work for something like: skip if
CHPL_AUX_FILESYS does not contain "lustre". It is possible to say: skip if
MY_VAR contains "some value".
Update error message to be more helpful.
Add test to exercise curl code.

This is a very simple test that opens a url, the github status api, and
verifies the FS type is correct.
Update .skipif logic to support "does not contain" operator.

Add new operator, >= (as opposed to <=), which mean <variable> does not contain
the substring <value>. For example, adding this line,
"CHPL_AUX_FILESYS >= lustre", to a skipif means: skip the test if
CHPL_AUX_FILESYS does not contain the substring "lustre".

I am not really happy with the operator, but I don't think it is any more or
less confusing than the <= operator.
Update skipifs for lustre and curl tests.
Merge pull request #591 from thomasvandoren/lustre-tests

Test to exercise lustre and curl code.

Add new tests that verifies FS type is lustre when CHPL_AUX_FILESYS
contains lustre and FS type is curl when CHPL_AUX_FILESYS contains
curl.

Also add new "does not contain" operator to skipif parser to support these
tests. The new operator, >= (as opposed to <=), means `<variable>` does
not contain the substring `<value>`. For example, adding this line to a skipif:

```
CHPL_AUX_FILESYS >= lustre
```

means: skip the test if CHPL_AUX_FILESYS environment variable does
not contain the substring "lustre". In other words, only the run the test if
lustre support is compiled.

I realize this operator is not exactly intuitive, but it's no more or less
intuitive than the "contains" operator, <=.