Status should be initialized as UNKNOWN instead of OK

[hrak]

The initial state of check.String() (which uses check.status) is OK while the initial check result is UNKNOWN. These should match.

// Initialize the check - this will return an UNKNOWN result
// until more results are added.
check := nagiosplugin.NewCheck()

fmt.Printf("%s", check.String())   // returns: 'OK'

check.Finish()  // returns 'UNKNOWN: no check result specified'

[stevemeier]

I have created a pull request to implement this.

As I understand the code, the Status is a uint which is initialized as 0, which maps to OK, according to Nagios standards.
I have changed this default value to be 3, which represents UNKNOWN.

I also had to change another piece of the code which seems to allow transition only "downwards":
OK -> WARNING -> ERROR -> UNKNOWN

With the new default being UNKNOWN, I changed this to allow transition from UNKNOWN to any other state.