command_tester.py: Print environment variables in a copy-and-pastable fashion
command_tester.py: Print environment variables in a copy-and-pastable fashion

Print the environment variables in the form:

  KEY1=value1 KEY2=value2 command arg1 arg2 ...

so that this can be easily copy-and-pasted into Bash.  Previously they
were only printed in the form:

  [KEY1] = value1
  [KEY2] = value2
  command arg1 arg2 ...

which is awkward to copy-and-paste.

Also simplify to use split() instead of find().

BUG=none
TEST=manually copy the command printed by (for example) run_mmap_test

Review URL: http://codereview.chromium.org/6504005

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@4299 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

sbc100/native_client,nacl-webkit/native_client,nacl-webkit/native_client,nacl-webkit/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,nacl-webkit/native_client,sbc100/native_client,nacl-webkit/native_client