test if flag is a bool before setting inFlag

[gmwxio]

Bug fix to get the following to work

cli --boolflag command

Currently command is attached to the boolean flag.
According to pflag
https://github.com/spf13/pflag#command-line-flag-syntax

// boolean or flags where the 'no option default value' is set
-f
-f=true
-abc
but
-b true is INVALID

Therefore boolean flags not set inFlag.

There seems to be inconsistencies is c.Flags() earlier on, hence adding the call to merge.
Also I don't understand why NoOptDefVal is not set for booleans as is appeared to be automatic by pflag.

[CLAassistant]

All committers have signed the CLA.

[dnephin]

Could you write a test that shows the bug?

[eparis]

If think you are saying that you have: flag.Value.Type() == "bool" but that flag.NoOptDefVal == "" I believe that shouldn't happen... Can you write a test how that happened.

[gmwxio]

@dnephin @eparis take a look at
https://github.com/wxio/cobra/tree/pr615test/tests

The issue may involve the combination of

var rootCmd = &cobra.Command{
	TraverseChildren: true,
}

and

var subCmd = &cobra.Command{
	Use:                "sub",
	DisableFlagParsing: true,
	Run: func(cmd *cobra.Command, args []string) {
		fmt.Printf("sub called with args %v", args)
	},
}

[gmwxio]

see #616