Use append_file in Redhat6xOSUtil.openssl_to_openssh()

[szarkos]

The ARM osprofile supports multiple SSH keys to embed into the user'ss
authorized_keys file. In DefaultOSUtil.openssl_to_openssh() we simply
run ssh-keygen and append ('>>') any public keys to the authorized_keys
file.

However, in older RHEL6 we did not have the PKCS8 module available with
ssh-keygen, so we wrote a different routine to handle this conversion
manually, Redhat6xOSUtil.openssl_to_openssh(). This function has a bug
that uses the write_file() utility function instead of append_file().
This fixes the bug.

Description

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[narrieta]

LGTM

Thank you for your contribution

[narrieta]

BVTs OK