[ST2 v3.3dev] Figure out if we can use the OS provided bats package or not

[blag]

Context: #428 (review)

In actions/setup_e2e_tests.sh, we install BATS from GitHub:

if [[ -n "$RHTEST" ]]; then
    ...
    # Install from GitHub
    # RHEL 7+ has both bats and jq package, so we don't need to do this once we
    # drop RHEL 6 support
    git clone --branch add_per_test_timing_information --depth 1 https://github.com/Kami/bats-core.git
    (cd bats-core; sudo ./install.sh /usr/local)
elif [[ -n "$DEBTEST" ]]; then
    ...
    # Install from GitHub
    git clone https://github.com/bats-core/bats-core.git
    (cd bats-core; sudo ./install.sh /usr/local)

As of this writing, the current release on GitHub is version v1.1.0.

However, if they are suitably up-to-date, we might be able to simply use the bats package provided by Ubuntu 16.04+. This would also afford us more control over our test environment by helping ensure that upgrades to upstream BATS master do not break our tests.

Further investigation needs to be done. A good time to do this, for both Ubuntu and RHEL OSes, will be once we drop RHEL 6 support, in version v3.3.