[cipd] Update CIPD client to v2.2.15.

This picks up the following changes:
d052999e15..20acb61858/cipd

R=tandrii@chromium.org, iannucci@chromium.org
BUG=915278

Change-Id: Ibaa9d20456dcb513d9bbdaf0bca970390254ee67
Reviewed-on: https://chromium-review.googlesource.com/c/1381773
Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
Commit-Queue: Vadim Shtayura <vadimsh@chromium.org>

cipd_client_version

@@ -1 +1 @@
-git_revision:03c4e813e09a23cd7004aca03aba32ad546d9202
+git_revision:6e4acf51a635665e54acaceb8bd073e5c7b8259a

cipd_client_version.digests

@@ -1,21 +1,21 @@
 # This file was generated by
 #
 #  cipd selfupdate-roll -version-file cipd_client_version \
-#      -version git_revision:03c4e813e09a23cd7004aca03aba32ad546d9202
+#      -version git_revision:6e4acf51a635665e54acaceb8bd073e5c7b8259a
 #
 # Do not modify manually. All changes will be overwritten.
 # Use 'cipd selfupdate-roll ...' to modify.
 
-linux-386       sha256  714bea642415e1c175eddce505e019a704a4f2acc1a21afa140d6318fb8d0401
-linux-amd64     sha256  8b2ce92994355c61e3693ccfd4f598b3cca685a1fa309051b871557d30d98da1
-linux-arm64     sha256  51ad96a8a31d6817a1fe9cfaaef39aa17ac50b426c9df5dc59138e9a8d571566
-linux-armv6l    sha256  fb7a3cd208f934b7d155db81ea54f3ea66512aafd6bc76d8930eb8750d1b8c52
-linux-mips64    sha256  ef5bb7d096822059b0f93dfb1d27156f44f201e5c96b577f8768e86dd71432b6
-linux-mips64le  sha256  6a7e8dd559db2e3c5e816874051f5c7191711f2d795eee7f832a721ae0db8315
-linux-mipsle    sha256  8a33ca853ce7ce9da0e9e2884e1ed3c8cea22c315a5c2ef53c8b40309e1cc5ab
-linux-ppc64     sha256  95213f2c5ed6048bd3cef026356f2eec13dfb1a26823b945bfef1c5bd6ece855
-linux-ppc64le   sha256  96548353376c97885ac6de2761dd9c9b4aee0a7b2a34ea056ba0a0f509be65be
-linux-s390x     sha256  0fc9d2f9324338122a22c7085e93bfee9a242d64fe95a0bd36a01818f39126b5
-mac-amd64       sha256  17671867253317f33af6363440a2cb0d881fe12ed6d24956d56322a38cfbdaae
-windows-386     sha256  2261420498cf0bf71a9f8e03a54f0e08033151d6f5f81d779aa78e553b586234
-windows-amd64   sha256  f7a3269f4d18c902f8a9b0954f4090d46f5c4f271381c3e563c5109043d552bb
+linux-386       sha256  bdb4e3c30cffddc650c791c78658b272173b638dc15aa74e2f1a28c41b5478bd
+linux-amd64     sha256  444addec6f9a87a3531519b404114e11a855cba41751be70c4383a0343e1e535
+linux-arm64     sha256  6cf92ce8ed3f5e0fafb44285cef777e5e7ffd50e4db892c0b25b06ea0accd7d5
+linux-armv6l    sha256  3f328f73191f3bd7f1e059f393929b341e99c9a33b7d49b96c8a87acd5df2b32
+linux-mips64    sha256  f5efa022177ae392621118a28bf04e59400960b392bc2ab49e321c6919728b28
+linux-mips64le  sha256  74067227f1c7123f0269588a1e910ffd5d6d806133fe62a1feeade27bde86bd3
+linux-mipsle    sha256  ecdc2fe38d10864e63bce742c105e816cec26237596b341a94e712fbbc482ef4
+linux-ppc64     sha256  d492b05890e57e1beeaa6161099aa5e1d3b7eec590cefbbd3ba221e9c99e5a6b
+linux-ppc64le   sha256  7a54d781defee4dbdaa5a5d2b2327af7cd3760e7ed8b3652a20f173998a925c4
+linux-s390x     sha256  802b8f6d8acf57fe656efd927439d8b6a475619b761aaa800b7909660ce91718
+mac-amd64       sha256  fc5fb99acd78c3a86ebf1d91b8198479d1cb3606f1594c0bb1e0d72d77ac3bb4
+windows-386     sha256  869d528a0d4b19e4226cd2cfc1da9984f29ed298130a4dc0da2f549f2a265961
+windows-amd64   sha256  82dda1326a2e7abfb6e8d5bc85548a1f0324d45dfecf9e4933a37c9148d90d20