server: terminal width should fallback to 80x25. (#1895)

Some environments might disable access to `/dev/tty`, fall
back to '80' in such scenarios.

Move to 'cheggaaa/pb' package for better cross platform
support on fetching terminal width.

Fixes #1891

vendor/github.com/cheggaaa/pb/reader.go

@@ -0,0 +1,17 @@
+package pb
+
+import (
+	"io"
+)
+
+// It's proxy reader, implement io.Reader
+type Reader struct {
+	io.Reader
+	bar *ProgressBar
+}
+
+func (r *Reader) Read(p []byte) (n int, err error) {
+	n, err = r.Reader.Read(p)
+	r.bar.Add(n)
+	return
+}