if anvil can't read the already installed cert, it will always replace them

[dlangille]

If /usr/local/etc/ssl is chmod 740 and chown root:wheel, anvil will not be able to read the certs. Therefore, the diff fails silently, and it always installs the certs.

proposed solution:

• test that file is readable
• if readable, proceed with diff
• if not readable, log error

[dlangille]

CERT_DST is the variable in question.