fix(plugin install): copy executable by renaming instead of create file

[c84c]

Implements

Fix #121

Discussion

During refactoring on commit change plugin build mechanism the new flogo executable is created instead of renamed.

Linux system not allows to update a running executable resulting in error text file busy.

The PR insert a SwapFile function to allow replacement of running executable (Thanks to @fenollp and his gist)

Code references

Old renaming implementation on commits before change plugin build mechanism :

cli/commands/plugin.go

Line 267 in 22cf3e3

err = os.Rename(filepath.Join(cliCmdPath, cliExe), exe)

Actual implementation on master:
Executable copy:

cli/commands/pluginhelper.go

Line 108 in 5c3e1e3

err = util.Copy(filepath.Join(cliCmdPath, cliExe), exPath, false)

copyFile function

cli/util/file.go

Lines 131 to 143 in 5c3e1e3

	var df *os.File
	if df, err = os.Create(dst); err != nil {
	return err
	}
	defer df.Close()
	if err = os.Chmod(sf.Name(), srcInfo.Mode()); err != nil {
	return err
	}
	if _, err = io.Copy(df, sf); err != nil {
	return err
	}

[c84c]

Have you planned when to merge the Pull Request?