Fix handling netns option in gen_udp

Bug found by Yaroslav Maslennikov and Andrei Pampukha.
Sort keys before generating

This has to be done in order to consistently generate the same
file so that we do not get rebuilds all the time.
erts: Use internal stack for ets db_has_variable
[ct_telnet] Don't send extra newline after password

The telnet client used to send an extra newline after the
password. This caused an extra prompt to be sent back from the
server. Some test cases failed every now and then due to this - since
the second promt was confusing. This is now corrected, i.e. the client
does no longer send an extra newline after the password.
[ct_telnet] Extend timeout in test from 1 to 2 sek

This is for stabilizing test cases.
[ct_telnet] Add timestamp to telnet_server debug printout

This is the telnet server used when testing ct_telnet and friends. The
telnet client itself is not changed.
[ct_telnet] Improve debug printouts and logging

ct_telnet_own_server_SUITE:large_string sometimes fail in the last
attempt - where get_data is used to fetch smaller chunks - probably
because one get_data message towards ct_telnet_client returns without
having received any new data.

This commit adds timestamps to debug printouts and improves the
logging.
[ct_telnet] Fix test case 'server_speaks'

This test case simulates that the server spontaneously sends data. By
changing ct_telnet:send to ct_telnet_client:send_data this simulations
makes more sense - since client's buffers are not flushed.

Also removed the newline at the end of "echo_no_prompt" command. Since
newline is added automatically, the explicit newline at the end of the
command causes a prompt to be sent which is not expected.
[ct_netconfc] Handle timeout failure in ssh

ssh_connection:subsystem/4 can return success | failure |
{error,timeout}. The latter was not handled by ct_netconfc.erl. This
is now corrected.
compiler: Coalesce map keys in dialyzer mode

This fixes a regression introduced in commit 805f9c89fc01220bc1bb0f27e1b68fd4eca688ba
The problem occured with map keys compiled with dialyzer option turned on.

In OTP 17, map keys needs to be literals.
dialyzer: Test recoalesced map keys
inets: stop httpc_handler on 'connection closed' send error

httpc_handler should be stopped when sending requests returns error
because of a closed connection and `tcp_closed` message could not be
catched (see http://erlang.org/pipermail/erlang-bugs/2007-May/000346.html )
otherwise it will lead to process leak.
inets: Fix typo
Update appup for 17.4

OTP-12196 remote request table leak
OTP-12233 3xxx result code without E-bit
OTP-12281 ignored connect_timer
OTP-12308 filter ordering
vsn -> 1.8
Text netns option at socket open
Merge branch 'lukas/erts/bif_info_rebuild/OTP-12344' into maint

* lukas/erts/bif_info_rebuild/OTP-12344:
  Sort keys before generating
Merge branch 'maint'

* maint:
  Sort keys before generating
erts: Fix finite warning for clang

clang aka llvm claims to be __GNUC__ and thus we have to
explicitly check that it is not used.
Merge branch 'lukas/erts/isfinite-fix/OTP-12268' into maint

* lukas/erts/isfinite-fix/OTP-12268:
  erts: Fix finite warning for clang