[Tizen] packaging: Explicitly specify our Python version as 2.7.

Tizen 2.1 (and possible later versions as well) use Python 2.7 instead of
2.6, so pass that to Chromium's python_arch.sh.

We were supposed to pass that ever since we started packaging Tizen, but
there are two things to take into account:

- The CPU architecture in python_arch.sh is only used to special-case some
  stuff for MIPS, so this wasn't impacting us negatively before.

- Things were still supposed to work even if we didn't specify
  `python_ver', but my own commit 211783 upstream has shown a bug in the
  file(1) shipped by Tizen 2.1: `file --dereference /does/not/exist' returns
  0 instead of 1, which made python_arch.sh follow a pathological code path.
Merge pull request #858 from rakuco/tizen-python_ver

[Tizen] packaging: Explicitly specify our Python version as 2.7.