sshcontrol: Use os.environ.copy() instead of copy.copy()

os.environ is special and copy.copy() doesn't do what we'd expect,
changes in the child object change the parent. copy.deepcopy() is
also known to have issues with it.

Use the dedicated .copy() method which will not influence the
parent. This fixes selftest failures where the DISPLAY variable
disappears.

(From OE-Core rev: 638cd44cc9a9eb435350aac7e8eeec585d74f8db)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oeqa/utils/sshcontrol.py

@@ -10,7 +10,6 @@ import subprocess
 import time
 import os
 import select
-import copy
 
 
 class SSHProcess(object):
@@ -33,7 +32,7 @@ class SSHProcess(object):
         self.logfile = None
 
         # Unset DISPLAY which means we won't trigger SSH_ASKPASS
-        env = copy.copy(os.environ)
+        env = os.environ.copy()
         if "DISPLAY" in env:
             del env['DISPLAY']
         self.options['env'] = env