DRY cin input_line (and test replacement of non-DRY usage)

src/common/command_line.cpp

@@ -3,9 +3,21 @@
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include "command_line.h"
+#include "string_tools.h"
 
 namespace command_line
 {
+  std::string input_line(const std::string& prompt)
+  {
+    std::cout << prompt;
+
+    std::string buf;
+    std::getline(std::cin, buf);
+
+    return epee::string_tools::trim(buf);
+
+  }
+
   const arg_descriptor<bool> arg_help = {"help", "Produce help message"};
   const arg_descriptor<bool> arg_version = {"version", "Output version information"};
   const arg_descriptor<std::string> arg_data_dir = {"data-dir", "Specify data directory"};