Install current version of jsonschema in CI

The build-unit-test-docker.sh script currently installs the jsonschema
Python package using apt-get.  This installs a fairly old version.

Change build-unit-test-docker.sh to use 'pip install' and 'pip3 install'
to install the current version of jsonschema instead.

Testing:
  * Ran CI interactively and verified current version of jsonschema
    installed.
  * Ran CI on phosphor-logging repository and verified tests passed.
  * Ran CI on phosphor-power repository and verified tests passed.

Signed-off-by: Shawn McCarney <shawnmm@us.ibm.com>
Change-Id: Id47a7c072763d5066f0ca18668ea942b5139454b
1 file changed