reproduce.tt: Add option to fetch but not build

Dependencies

• [2] 5Q4ZLL37 reproduce.tt: Add --help flag
• [*] HZWUT4YN Allow users to reproduce builds on their own systems

Change contents

• edit in src/root/reproduce.tt at line 18
  [2.124]

  [2.124]
  + fetchOnly=
• edit in src/root/reproduce.tt at line 46
  [2.1078]

  [2.1078]
  +

  + --fetch

  + Fetch the inputs and then exit.
• edit in src/root/reproduce.tt at line 61
  [2.1373]

  [2.1373]
  + elif [ "$arg" = --fetch ]; then

  + fetchOnly=1
• edit in src/root/reproduce.tt at line 174
  [4.3144]

  [4.3144]
  +

  + if [ -n "$fetchOnly" ]; then exit 0; fi