tests/test-install.t

test-obsolete: use 'log -T {node}' instead of 'id --debug -i' to lookup hash

I ran into a case when adding a test where there were cryptic hg command line
errors.  I eventually traced it back to 'hg id' printing debug messages before
the hash:

    invalid branchheads cache (served): tip differs <hash>

This method should eliminate any other output except the node.

hg debuginstall
  $ hg debuginstall
  checking encoding (ascii)...
  checking Python executable (*) (glob)
  checking Python version (2.*) (glob)
  checking Python lib (*lib*)... (glob)
  checking installed modules (*mercurial)... (glob)
  checking templates (*mercurial?templates)... (glob)
  checking commit editor...
  checking username...
  no problems detected

hg debuginstall with no username
  $ HGUSER= hg debuginstall
  checking encoding (ascii)...
  checking Python executable (*) (glob)
  checking Python version (2.*) (glob)
  checking Python lib (*lib*)... (glob)
  checking installed modules (*mercurial)... (glob)
  checking templates (*mercurial?templates)... (glob)
  checking commit editor...
  checking username...
   no username supplied
   (specify a username in your configuration file)
  1 problems detected, please check your install!
  [1]