Fix empty values in osfamilymap.yaml

[myii]

In the process of providing #228, encountered a number of empty values that were difficult to resolve. See #228 (comment). Got around this by using inline ignores but these still need to be resolved from a formula perspective, as well as yamllint:

mysql-formula/mysql/osfamilymap.yaml

Lines 66 to 73 in 70e5b43

	# Empty values below to be resolved, disabling the rule in the meantime
	# yamllint disable rule:empty-values
	port:
	user:
	socket:
	datadir:
	tmpdir:
	# yamllint enable rule:empty-values

mysql-formula/mysql/osfamilymap.yaml

Lines 90 to 92 in 70e5b43

	# Empty value below to be resolved, disabling the rule in the meantime
	# yamllint disable-line rule:empty-values
	dev:

mysql-formula/mysql/osfamilymap.yaml

Lines 221 to 225 in 70e5b43

	# Empty values below to be resolved, disabling the rule in the meantime
	# yamllint disable rule:empty-values
	user:
	datadir:
	# yamllint enable rule:empty-values

CC: @noelmcloughlin.