Cleaned cross-compile configure script.

Trying to remove ambiguity and not used environment variables.
Removed .zin and .zdist files.

From now will maintain original "pre-config"  files without duplicating. If we 
need some change just modify them, there is no need to keep original versions.
Disable build host python.

We assume build environment already have python installed. Anyway,
it's only needed for 'install' phase.
Left pgen build untouched for now. First, it's object files are included in 
libpython.a which may be needed. Next, no reasonable substitute is found.
Cleaning build scripts.
Replace compiling python with host python.

We're going not to compile python for host. It's only needed
for shared build and setup/install phases.
Assume we already have host python which could be
invoked to do installation (no shared build, anyway).
Fixes zerovm/zpython2#1.

Disabling shared modules build and install broke `exec_prefix`
directory structure creating. It lead to broken python installation
during python runtime configuration step.

Python uses `lib-dynload` as landmark for detecting `exec_prefix`.
Now fixing it.
Replaced bunch of build scripts with one.

Get rid of separate configure/compile/rebuild scripts in favour
of one: 2build_zpython.sh.

Building zpython2 has now only 2 phases: building pgen and
compiling python itself.
Merge pull request #2 from rampage644/master

Build process + fixed issue#1