use full path on commands

[skpy]

On a RHEL7 host, this module fails to install pip with the following Hiera settings:

python::pip: present
python::provider: 'pip'
python::use_epel: false

The errors are:

==> g2: Error: Parameter unless failed on Exec[bootstrap pip]: 'which pip' is not qualified and no path was specified. Please qualify the command or specify a path. at /tmp/vagrant-puppet/modules-748e6aae0e9d5fc067b3ca7dd8f9d74d/python/manifests/install.pp:75

and

==> g2: Error: Validation of Exec[bootstrap pip] failed: 'curl https://bootstrap.pypa.io/get-pip.py | python' is not qualified and no path was specified. Please qualify the command or specify a path. at /tmp/vagrant-puppet/modules-748e6aae0e9d5fc067b3ca7dd8f9d74d/python/manifests/install.pp:75

This PR simply puts the full path to the executables, which resolves the errors.