feat(cli/run): read inputs from file/cmdline (#180)

This diff introduces the possibility of specifying --input-file file
multiple times to force ooniprobe to read inputs from file.

Like we do for miniooni, the file shall contain a single entry per
line and this entry should be a URL for websites.

Likewise, one can specify --input URL multiple times.

This implementation is a very simple, initial implementation and there
is a bunch of changes I'd like to add on top of it.

And also perhaps a bunch of cleanups.

I've chosen to expose these flag _only_ for websites for now.

Part of https://github.com/ooni/probe/issues/1283.

internal/nettests/nettests.go

@@ -44,6 +44,15 @@ type Controller struct {
 	msmts       map[int64]*database.Measurement
 	inputIdxMap map[int64]int64 // Used to map mk idx to database id
 
+	// InputFiles optionally contains the names of the input
+	// files to read inputs from (only for nettests that take
+	// inputs, of course)
+	InputFiles []string
+
+	// Inputs contains inputs to be tested. These are specified
+	// using the command line using the --input flag.
+	Inputs []string
+
 	// numInputs is the total number of inputs
 	numInputs int
 

internal/nettests/web_connectivity.go

@@ -12,6 +12,8 @@ func lookupURLs(ctl *Controller, limit int64, categories []string) ([]string, ma
 	inputloader := engine.NewInputLoader(engine.InputLoaderConfig{
 		InputPolicy:   engine.InputRequired,
 		Session:       ctl.Session,
+		SourceFiles:   ctl.InputFiles,
+		StaticInputs:  ctl.Inputs,
 		URLCategories: categories,
 		URLLimit:      limit,
 	})