util: Rename virFileHasSuffix() to virStringHasCaseSuffix()

Despite its name, this is really just a general-purpose string
manipulation function, so it should be moved to the virstring
module and renamed accordingly.

In addition to the obvious s/File/String/, also tweak the name
to make it clear that the presence of the suffix is verified
using case-insensitive comparison.

A few trivial whitespace changes are squashed in.

Signed-off-by: Andrea Bolognani <abologna@redhat.com>
ACKed-by: Peter Krempa <pkrempa@redhat.com>

tests/testutils.c

@@ -525,8 +525,8 @@ virTestRewrapFile(const char *filename)
     char *script = NULL;
     virCommandPtr cmd = NULL;
 
-    if (!(virFileHasSuffix(filename, ".args") ||
-          virFileHasSuffix(filename, ".ldargs")))
+    if (!(virStringHasCaseSuffix(filename, ".args") ||
+          virStringHasCaseSuffix(filename, ".ldargs")))
         return 0;
 
     if (!perl) {