crypto: make getCiphers() return non-SSL ciphers

Commit f53441a added crypto.getCiphers() as a function that returns the
names of SSL ciphers.

Commit 14a6c4e then added crypto.getHashes(), which returns the names of
digest algorithms, but that creates a subtle inconsistency: the return
values of crypto.getHashes() are valid arguments to crypto.createHash()
but that is not true for crypto.getCiphers() - the returned values are
only valid for SSL/TLS functions.

Rectify that by adding tls.getCiphers() and making crypto.getCiphers()
return proper cipher names.

Reviewers: @indutny @isaacs

Submitted for the v0.10 branch because I see it as a bug fix. Opinions?