Power user command support for directory scans (#467)

* Power-user directory source support
Signed-off-by: Mikey Strauss <mikey@scribe-security.com>

Signed-off-by: houdini91 <mdstrauss91@gmail.com>

* Remove newline

Signed-off-by: houdini91 <mdstrauss91@gmail.com>

* Shared filetree (#1)

* Shared directory resolver filetree

Signed-off-by: houdini91 <mdstrauss91@gmail.com>

* PR - change error ErrObserve to ErrPath

Signed-off-by: houdini91 <mdstrauss91@gmail.com>

* PR - share directory resolver
* Use pointer to source struct

Signed-off-by: houdini91 <mdstrauss91@gmail.com>

* Fix Lint

Signed-off-by: houdini91 <mdstrauss91@gmail.com>

internal/err_helper.go

@@ -1,7 +1,9 @@
 package internal
 
 import (
+	"fmt"
 	"io"
+	"os"
 
 	"github.com/anchore/syft/internal/log"
 )
@@ -12,3 +14,25 @@ func CloseAndLogError(closer io.Closer, location string) {
 		log.Warnf("unable to close file for location=%q: %+v", location, err)
 	}
 }
+
+type ErrPath struct {
+	Path string
+	Err  error
+}
+
+func (e ErrPath) Error() string {
+	return fmt.Sprintf("unable to observe contents of %+v: %v", e.Path, e.Err)
+}
+
+func IsErrPath(err error) bool {
+	_, ok := err.(ErrPath)
+	return ok
+}
+
+func IsErrPathPermission(err error) bool {
+	pathErr, ok := err.(ErrPath)
+	if ok {
+		return os.IsPermission(pathErr.Err)
+	}
+	return ok
+}