Fix tox invocation errors caused by sitepackages.

sitepackages was set to True in tox.ini which allowed an error to occur
when global packages were modified. Added new files to tox ignore and
added funcsigs (used by mock) to setup.py

setup.py

@@ -50,7 +50,8 @@ def publish():
     setup_requires=[
         'coverage==3.7.1',
         'nose==1.3.1',
-        'mock==1.1.2'
+        'mock==1.1.2',
+        'funcsigs==0.4'
     ],
     package_dir={'pygatt': 'pygatt'},
     zip_safe=False,

tox.ini

@@ -7,7 +7,6 @@
 envlist = py27
 
 [testenv]
-sitepackages=True
 commands =
     {envpython} setup.py nosetests
     flake8
@@ -17,4 +16,4 @@ passenv = PROGRAMFILES
 
 [flake8]
 max-line-length = 80
-exclude=.coverage,.eggs,.git,.gitignore,.tox,.travis.yml,coverage*, nose*,include,Include,LICENSE,lib,local,Lib,MANIFEST.in,Makefile,NOTICE, README.rst,bin,Scripts,build,cover,dist,docs,man, nostests.xm., pip-selfcheck.json,pygatt.egg-info,requirements.txt,setup.py,setup.cfg,tox.ini
+exclude=.coverage,*.egg,.eggs,.git,.gitignore,.tox,.travis.yml,coverage*, nose*,include,Include,LICENSE,lib,local,Lib,MANIFEST.in,Makefile,NOTICE, README.rst,bin,Scripts,build,cover,dist,docs,man, nostests.xm., pip-selfcheck.json,pygatt.egg-info,requirements.txt,setup.py,setup.cfg,tox.ini