Adding service_name attribute

Allows for customization of the service names depending on how the package defines the service name.
Default values set to "ossec-hids-server" and "ossec-hids-client"
Updating service_name
Updating service_name client
Documenting server_name usage

Added server_name attributes to ossec-server and ossec-agent sections.
Fixed ossec-agent attribute in README.md
fixed typo in service_name variable.
fixed typo in service_name variable.
fixed typo in service_name variable.
Merge pull request #6 from swarren83/patch-3

Adding service_name attribute