Introduce sphere-installation, the canonical way to determine the path to the current sphere installation.
Introduce sphere-installation, the canonical way to determine the path to the current sphere installation.

Either: answers the value of sphere_installDirectory or answers the parent directory of the
directory containing the sphere-installation script, assuming that if sphere-installation is in the
path it is within the bin directory of the installation.

Because: snappy.

Signed-off-by: Jon Seymour <44f878afe53efc66b76772bd845eb65944ed8232@ninjablocks.com>

ninjasphere/sphere-global-utils