Crash when relative path is given for SQLite db
```
(venv) xazax@cc:~/Checker_Xerces$ CodeChecker server --sqlite db.sqlite --not-host-only -v 15010
Traceback (most recent call last):
  File "/mnt/storage/xazax/Checker_Xerces/codechecker/build/CodeChecker/cc_bin/CodeChecker.py", line 101, in main
    args.func(args)
  File "/mnt/storage/xazax/Checker_Xerces/codechecker/build/CodeChecker/lib/python2.7/libcodechecker/libhandlers/server.py", line 332, in __handle
    main(args)
  File "/mnt/storage/xazax/Checker_Xerces/codechecker/build/CodeChecker/lib/python2.7/libcodechecker/libhandlers/server.py", line 414, in main
    os.makedirs(os.path.dirname(args.sqlite))
  File "/mnt/storage/xazax/Checker_Xerces/codechecker/venv/lib/python2.7/os.py", line 157, in makedirs
    mkdir(name, mode)
OSError: [Errno 2] No such file or directory: ''
```
Also, default product is not created. Is this bug or intended?
diff --git a/web/server/codechecker_server/cmd/server.py b/web/server/codechecker_server/cmd/server.py
index 10236f47..23b85b0c 100644
--- a/web/server/codechecker_server/cmd/server.py
+++ b/web/server/codechecker_server/cmd/server.py
@@ -394,6 +394,10 @@ def add_arguments_to_parser(parser):
             args.sqlite = args.sqlite.replace('<CONFIG_DIRECTORY>',
                                               args.config_directory)
 
+        # Convert relative sqlite file path to absolute.
+        if 'sqlite' in args:
+            args.sqlite = os.path.abspath(args.sqlite)
+
         if 'postgresql' not in args:
             # Later called database modules need the argument to be actually
             # present, even though the default is suppressed in the optstring.
['web/server/codechecker_server/cmd/server.py']