status: Use bold more sparsely at -v1.

Until now, at -v1, all the "apply N grafts" messages (for instance)
would be displayed in bold.  This would typically result in several
subsequent lines all bold, although none of them is particularly
interesting.  This improves on that by avoiding bold at -v1 for these
messages.

* guix/status.scm (print-build-event)[emph]: New variable.
Use it for the "View build log", "expected hash", and "offloading build"
messages.
[info]: Default to 'identity' when PRINT-URLS? and PRINT-LOG? are both
false.

guix/status.scm

@@ -414,6 +414,11 @@ (define* (print-build-event event old-status status
 addition to build events.  When PRINT-URLS? is true, display the URL of
 substitutes being downloaded."
   (define info
+    (if (and colorize? (or print-urls? print-log?))
+        (cute colorize-string <> (color BOLD))
+        identity))
+
+  (define emph
     (if colorize?
         (cute colorize-string <> (color BOLD))
         identity))
@@ -526,7 +531,7 @@ (define erase-current-line*
         (format port (failure (G_ "Could not find build log for '~a'."))
                 drv))
        (log
-        (format port (info (G_ "View build log at '~a'.")) log)))
+        (format port (emph (G_ "View build log at '~a'.")) log)))
      (newline port))
     (('substituter-started item _ ...)
      (erase-current-line*)
@@ -577,12 +582,12 @@ (define erase-current-line*
      ;; /gnu/store/…-sth:", where "sha256" is the hash algorithm.
      (format port (failure (G_ "~a hash mismatch for ~a:")) algo item)
      (newline port)
-     (format port (info (G_ "\
+     (format port (emph (G_ "\
   expected hash: ~a
   actual hash:   ~a~%"))
              expected actual))
     (('build-remote drv host _ ...)
-     (format port (info (G_ "offloading build of ~a to '~a'")) drv host)
+     (format port (emph (G_ "offloading build of ~a to '~a'")) drv host)
      (newline port))
     (('build-log pid line)
      (if (multiplexed-output-supported?)