…ew one.

Problem: When cc_ca_certs configuration has both "remove-defaults: true"
and also specifies one, or more, new trusted CAs to add then the resultant
/etc/ca-certificates.conf file's 1st line is blank. As noted in comments
in the existing cc_ca_certs.py code blank lines in this file cause problems.

Fix: Before adding the cloud-init CA filename to this file first check the
size of the file - if is is empty (as all existing CAs have been deleted)
then write only the cloud-init CA filename to the file rather than appending
it to the file.

…ng new one

Existing testcases do not handle the situation where all the existing CA
certs are deleted (so resulting in an empty /etc/ca-certificates.conf file
and when one, or more, new CAs are added). This testcase verifies that the
resultant ca-certificates.conf file does not contain any blank lines which
are known to cause problems for the update-ca-certificates utility.

… zero size.

… errors