use context manager for stdin files and use _put_file_shell

requires https://gerrit.opnfv.org/gerrit/#/c/25183/

use new ssh method _put_file_shell to upload files.
We have to use _put_file_shell because we rely on ~/ path
expansions.  Eventually we should move to remote absolute
paths so we can use sftp upload.

For ssh.execute() replace open() with context manager

context managers were invented partly to control
freeing resources.  Opening files without closing
them will leak file descriptors.

The old standard method for closing files:

f = open('data.txt')
try:
    data = f.read()
finally:
    f.close()

was replaced with a context manager

with open('data.txt') as f:
    data = f.read()

Reference:  Raymond Hettinger's Pycon 2013 presentation:
https://speakerdeck.com/pyconslides/transforming-code-into-beautiful-idiomatic-python-by-raymond-hettinger-1

Video: https://youtu.be/OSGv2VnC0go?t=2522

Always use context managers for files

Update:
   rebased now that _put_file_shell was merged

Change-Id: Iabfc0e43aa3b7766d7c658115e13d21c31efb2a9
Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>

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