Fix EnumVarP func to show default value associated with EnumVariable …

[RamanaReddy0M]

…(#104)

[tarunKoyalwar]

lgtm!

[Mzack9999]

suggesting stricter check on enum values

[tarunKoyalwar]

@Mzack9999 , what do you thing about changing default value type and AllowedTypes?

Current Implementation

flagSet.EnumVarP(&options.ScanStrategy, "scan-strategy", "ss", goflags.EnumVariable(0), "strategy to use while scanning(auto/host-spray/template-spray)", goflags.AllowdTypes{
			"auto":           goflags.EnumVariable(0),
			"host-spray":     goflags.EnumVariable(1),
			"template-spray": goflags.EnumVariable(2),
		})

New Implementation

flagSet.EnumVarP(&options.ScanStrategy, "scan-strategy", "ss", "auto", "strategy to use while scanning(auto/host-spray/template-spray)", []string{"auto","host-spray","template-spray"}

we will use Allowd Types internally but there doesn't seem a need to expose it and make it complex .
and for validation we can simply do

if _,ok:= AllowedTypes[defaultValue]; !ok{
    panic(fmt.Errof("%v does not belong to %v",defaultValue,AllowedTypes))
}

[Mzack9999]

@tarunKoyalwar That's what I was discussing with @RamanaReddy0M , I think anyway that a iota allows to plug in more generic implementations. Internally it's needed some refactoring as also other types like boolean/ints are considered like strings, losing their original type