Low priority: `sys.excepthook is missing` on RHEL 7

When installing ST2 2.3 or 2.4dev on RHEL 7.4 with the one-line install script, early in the installation we see this output:

########################################################
          Installing st2 stable
########################################################
Loaded plugins: amazon-id, rhui-lb, search-disabled-repos
Package net-tools-2.0-0.22.20131004git.el7.x86_64 already installed and latest version
Nothing to do
Loaded plugins: amazon-id, rhui-lb, search-disabled-repos
Package policycoreutils-python-2.5-17.1.el7.x86_64 already installed and latest version
Nothing to do
close failed in file object destructor:
sys.excepthook is missing
lost sys.stderr
Loaded plugins: amazon-id, rhui-lb, search-disabled-repos
Package yum-utils-1.1.31-42.el7.noarch already installed and latest version
Nothing to do

This comes from this line in the bootstrap script:

    # Allow rabbitmq to use '25672' port, otherwise it will fail to start
    sudo semanage port --list | grep -q 25672 || sudo semanage port -a -t amqp_port_t -p tcp 25672

When running this manually, we can see that this results in an error:

ec2-user@ip-10-0-4-161 ~]$ sudo semanage port --list | grep -q 25672
close failed in file object destructor:
sys.excepthook is missing
lost sys.stderr
[ec2-user@ip-10-0-4-161 ~]$

It appears to be the same problem as referenced here

The underlying problem is related to semanage, but it only shows up when passed to grep -q.

As a workaround, we could do something like this:

sudo semanage port --list | grep 25672 > /dev/null || sudo semanage port -a -t amqp_port_t -p tcp 25672

Not quite as elegant, but it gets the job done.

Start in scripts/st2bootstrap-el7.sh at line 170 and reproduce the semanage port --list pipeline on RHEL 7. Compare the grep -q command with the proposed /dev/null workaround. Done means the bootstrap no longer emits the sys.excepthook or lost sys.stderr messages while still adding port 25672 when it is absent.