[tests] search for fixed strings, not regexps, by default

Change grep_for_content to grep for a fixed string by default.

The reason is tests would match 1a2b3c4 as IP address 1.2.3.4 (which it
is not).

Add regexp option to grep_for_content, to allow the default "grep" search.

Resolves: #3320

Signed-off-by: Pavel Moravec <pmoravec@redhat.com>

tests/sos_tests.py

@@ -390,11 +390,16 @@ def _decrypt_archive(self, archive):
             raise
         return _archive
 
-    def grep_for_content(self, search):
+    def grep_for_content(self, search, regexp=False):
         """Call out to grep for finding a specific string 'search' in any place
         in the archive
+
+        :param search: string to search
+        :param regexp: use regular expression search (default False
+                       means "grep -F")
         """
-        cmd = "grep -ril '%s' %s" % (search, self.archive_path)
+        fixed_opt = "" if regexp else "F"
+        cmd = "grep -ril%s '%s' %s" % (fixed_opt, search, self.archive_path)
         try:
             out = process.run(cmd)
             rc = out.exit_status