python-lvm: Memory leaks & seg. fault fixes

python-lvm: Memory leaks & seg. fault fixes

Issues found (thus far) in unit test developemnt for python bindings.

Added Py_DECREF(ptr) in liblvm_lvm_vg_open & liblvm_lvm_vg_create
in error paths so that we correctly clean up memory.

Added a call to lvm_vg_close when we remove a vg.  The code was
clearing out the vg pointer which prevented us from actually
calling lvm_vg_close in the close path.

liblvm_lvm_vg_create_lv_linear was not initializing
lvobj->parent_vgobj and if lvm_vg_create_lv_linear failed
we went through liblvm_lv_dealloc on clean up and tried to
Py_DECREF an invalid pointer.

Signed-off-by: Tony Asleson <tasleson@redhat.com>