recipetool: Handle several go-import tags in go resolver

When dynamically resolving go modules, the HTML page may contain several
go-import meta tags. We must handle all and pick the correct one based
on the module name. An example for such a behaviour is
gonum.org/v1/gonum:

<meta name="go-import" content="gonum.org/v1/exp git https://github.com/gonum/exp">
<meta name="go-import" content="gonum.org/v1/gonum git https://github.com/gonum/gonum">
<meta name="go-import" content="gonum.org/v1/hdf5 git https://github.com/gonum/hdf5">
<meta name="go-import" content="gonum.org/v1/netlib git https://github.com/gonum/netlib">
<meta name="go-import" content="gonum.org/v1/plot git https://github.com/gonum/plot">
<meta name="go-import" content="gonum.org/v1/tools git https://github.com/gonum/tools

">

Signed-off-by: Sven Schwermer <sven.schwermer@disruptive-technologies.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>