Allow OSError to skip scriptdir removal

On Ubuntu the scriptdir gets placed into sys.path.  This makes some
modules (copy) fail because the ansible module gets loaded instead of
the stdlib copy module.  So we remove scriptdir there.  Unfortunately,
the scriptdir code uses abspath().  When pipelining, abspath() has to
find the cwd.  On OSX, finding the cwd when that directory is not
executable by the user raises an OSError.  Since OSX does not suffer
from the scriptdir problem we're able to just skip scriptdir handling if
we get that exception.

Fixes #19729

lib/ansible/executor/module_common.py

@@ -107,10 +107,21 @@
 # Ubuntu15.10 with python2.7  Works
 # Ubuntu15.10 with python3.4  Fails without this
 # Ubuntu16.04.1 with python3.5  Fails without this
+# To test on another platform:
+# * use the copy module (since this shadows the stdlib copy module)
+# * Turn off pipelining
+# * Make sure that the destination file does not exist
+# * ansible ubuntu16-test -m copy -a 'src=/etc/motd dest=/var/tmp/m'
+# This will traceback in shutil.  Looking at the complete traceback will show
+# that shutil is importing copy which finds the ansible module instead of the
+# stdlib module
 scriptdir = None
 try:
     scriptdir = os.path.dirname(os.path.abspath(__main__.__file__))
-except AttributeError:
+except (AttributeError, OSError):
+    # Some platforms don't set __file__ when reading from stdin
+    # OSX raises OSError if using abspath() in a directory we don't have
+    # permission to read.
     pass
 if scriptdir is not None:
     sys.path = [p for p in sys.path if p != scriptdir]