devserver: allow calling devserver from anywhere

Change-Id: I5b1eaf2d2d2bc1ee51d0ff676e2a64abc98b1322

BUG=5246
TEST=below
1) Modified unittests to run from /
2) Ran unit tests before the change and saw the fail
3) Ran unit tests after the change and saw them succeed
4) sudo FEATURES=test ACCEPT_KEYWORDS=~amd64 emerge cros-devutils (see things installed and unittests passing)

Review URL: http://codereview.chromium.org/6425002
diff --git a/devserver.py b/devserver.py
index 47a576c..9d4b87e 100755
--- a/devserver.py
+++ b/devserver.py
@@ -30,7 +30,8 @@
                     'server.socket_port': int(options.port),
                     'server.socket_timeout': 6000,
                     'response.timeout': 6000,
-                    'tools.staticdir.root': os.getcwd(),
+                    'tools.staticdir.root':
+                      os.path.dirname(os.path.abspath(sys.argv[0])),
                   },
                   '/build':
                   {