Could not add community index with git 2.7.4

[JeremyGrosser]

As reported on StackOverflow: on Ubuntu 16.04 with git version 2.7.4, alire fails to checkout the community index while trying to run git submodule update --init --recursive --progress

I believe the --progress flag is relatively new and not supported by old versions of git. Could we remove this flag to make alire more compatible with older distros?

I was able to reproduce this issue inside a docker container with the ubuntu:16.04 base image.

root@520192a5c2b3:/hello_pico# alr -d with pico_bsp
Cloning into '/root/.config/alire/indexes/community/repo'...
remote: Enumerating objects: 6443, done.
remote: Counting objects: 100% (1625/1625), done.
remote: Compressing objects: 100% (943/943), done.
remote: Total 6443 (delta 777), reused 1161 (delta 486), pack-reused 4818
Receiving objects: 100% (6443/6443), 1.05 MiB | 0 bytes/s, done.
Resolving deltas: 100% (3594/3594), done.
Checking connectivity... done.
usage: git submodule [--quiet] add [-b <branch>] [-f|--force] [--name <name>] [--reference <repository>] [--] <repository> [<path>]
   or: git submodule [--quiet] status [--cached] [--recursive] [--] [<path>...]
   or: git submodule [--quiet] init [--] [<path>...]
   or: git submodule [--quiet] deinit [-f|--force] [--] <path>...
   or: git submodule [--quiet] update [--init] [--remote] [-N|--no-fetch] [-f|--force] [--checkout|--merge|--rebase] [--reference <repository>] [--recursive] [--] [<path>...]
   or: git submodule [--quiet] summary [--cached|--files] [--summary-limit <n>] [commit] [--] [<path>...]
   or: git submodule [--quiet] foreach [--recursive] <command>
   or: git submodule [--quiet] sync [--recursive] [--] [<path>...]
stderr: Command ["git", "submodule", "update", "--init", "--recursive", "--progress"] exited with code 1
stderr: Generating Outcome_Failure with message: Command ["git", "submodule", "update", "--init", "--recursive", "--progress"] exited with code 1
stderr: Generating Outcome_Failure with call stack:
stderr: raised AAA.DEBUG.STACK_TRACE.DEBUG_EXCEPTION : aaa-debug.adb:44
[/bin/alr]
0xde957a Aaa.Debug.Stack_Trace at aaa-debug.adb:44
0xce4b97 Alire.Outcome_Failure at alire.adb:174
0x7a9a48 Alire.Errors.Get at alire-errors.adb:101
0xcbd545 Alire.Vcss.Git.Clone at alire-vcss-git.adb:122
0xcbb5a6 Alire.Vcss.Git.Clone at alire-vcss-git.adb:69
0x8e4d40 Alire.Index_On_Disk.Git.Add at alire-index_on_disk-git.adb:11
0x8e7301 Alire.Index_On_Disk.Add_With_Metadata at alire-index_on_disk.adb:62
0x890f4d Alire.Features.Index.Add at alire-features-index.adb:139
0x89485f Alire.Features.Index.Add_Or_Reset_Community at alire-features-index.adb:174
0x8956cf Alire.Features.Index.Setup_And_Load at alire-features-index.adb:210
0x514e2c Alr.Commands.Requires_Full_Index at alr-commands.adb:224
0x5151b2 Alr.Commands.Requires_Valid_Session at alr-commands.adb:261
0x4ddbe7 Alr.Commands.Withing.Execute at alr-commands-withing.adb:241
0x50dadf Alr.Commands.Sub_Cmd.Execute at clic-subcommand-instance.adb:592
0x516b66 Alr.Commands.Execute at alr-commands.adb:410
0x427e3c Alr.Main at alr-main.adb:28
0x42a841 Main at b__alr-main.adb:2070
[/lib/x86_64-linux-gnu/libc.so.6]
0x7f8c2883483e
[/bin/alr]
0x427a68 _start at ???
0xfffffffffffffffe

stderr: Failed Outcome because of exception: 
stderr: Command ["git", "submodule", "update", "--init", "--recursive", "--progress"] exited with code 1
stderr: raised ALIRE.CHECKED_ERROR : alire-stored-error:2
[/bin/alr]
0xce33cd Alire.Assert at alire.adb:110
0x8e7313 Alire.Index_On_Disk.Add_With_Metadata at alire-index_on_disk.adb:62
0x890f4d Alire.Features.Index.Add at alire-features-index.adb:139
0x89485f Alire.Features.Index.Add_Or_Reset_Community at alire-features-index.adb:174
0x8956cf Alire.Features.Index.Setup_And_Load at alire-features-index.adb:210
0x514e2c Alr.Commands.Requires_Full_Index at alr-commands.adb:224
0x5151b2 Alr.Commands.Requires_Valid_Session at alr-commands.adb:261
0x4ddbe7 Alr.Commands.Withing.Execute at alr-commands-withing.adb:241
0x50dadf Alr.Commands.Sub_Cmd.Execute at clic-subcommand-instance.adb:592
0x516b66 Alr.Commands.Execute at alr-commands.adb:410
0x427e3c Alr.Main at alr-main.adb:28
0x42a841 Main at b__alr-main.adb:2070
[/lib/x86_64-linux-gnu/libc.so.6]
0x7f8c2883483e
[/bin/alr]
0x427a68 _start at ???
0xfffffffffffffffe

stderr: Could not add community index: Command ["git", "submodule", "update", "--init", "--recursive", "--progress"] exited with code 1
error: Could not add community index: Command ["git", "submodule", "update", "--init", "--recursive", "--progress"] exited with code 1